This invention relates to resid hydrotreating and, more particularly, to a process to minimize catalyst slumping.
In the past, fluctuations of supply, demand, costs, and prices of oil have created instability and uncertainty for net oil consuming countries, such as the United States, to attain adequate supplies of high-quality, low-sulfur, petroleum crude oil (sweet crude) from Saudi Arabia and other countries at reasonable prices for conversion into gasoline, fuel oil, and petrochemical feed-stocks. In an effort to stabilize the supply and availability of crude oil at reasonable prices, Amoco Oil Company has developed constructed and commercialized extensive, multimillion dollar refinery projects under the Second Crude Replacement Program (CRP II) to process poorer quality, high-sulfur, petroleum crude oil (sour crude) and demetallate, desulfurize, and hydrocrack resid to produce high-value products, such as gasoline, distillates, catalytic cracker feed, metallurgical coke, and petrochemical feedstocks. The Crude Replacement Program is of great benefit to the oil-consuming nations by providing for the availability of adequate supplies of gasoline and other petroleum products at reasonable prices while protecting the downstream operations of refining companies.
During resid hydrotreating, a bed of hydrotreating catalyst is expanded by circulating oil through the bed, and resid oil (resid) mixed with hydrogen-rich gases and passed through the catalyst bed in a three-phase mixture of oil, catalyst, and gas bubbles to produce more valuable lower-boiling liquid products. Over time, in many units, however, significant amounts of catalyst often slump, cluster, agglomerate, build up, adhere, and stick to the walls of the reactor, downcomer and grid. Slumping catalyst piles up and does not circulate and expand nor does it effectively mix or promote the reaction of the oil and gases. Furthermore, slumping catalyst can block the flow of oil and gases, reduce available reactor volume, and become stagnant, inactive, and ineffective.
Catalyst agglomeration decreases the efficiency of hydrotreating and diminishes the conversion of resid to more valuable lower-boiling liquid products. Catalyst buildup and clustering can cause the catalyst bed to become unstable. It can also cause excess gas channeling, stagnant zones, and loss of product quality. Furthermore, catalyst accumulation and piling against the walls can cause the oil (resid) to channel (rise) faster up one side of the reactor than the other and increase the maldistribution of the oil and gases. In extreme cases, catalyst slumping can cause hot spots which can rupture the vessel wall.
Catalyst buildup and slumping can also accelerate coke formation and plug up the grid as well as the outlet and inlet lines. It can lead to premature shutdown, extended downtime, and increased frequency of maintenance and repair. Increased maintenance and repair requires additional manpower and is time consuming, tedious, and expensive. It further decreases the reactor's efficiency and adversely affects the operability, performance, and profitability of the unit.
Over the years, various processes and equipment have been suggested or developed to increase the efficiency of hydrotreating resid and/or processing other hydrocarbons. Typifying such prior art processes and equipment are those found in U.S. Pat. Nos. 2,425,098; 2,910,425; 2,934,411; 3,104,155; 3,227,527; 3,288,567; 3,527,575; 3,607,127; 3,904,549; 4,035,152; 4,135,889; 4,414,100; 4,320,089; 4,510,021; 4,661,265; 4,662,669; 4,715,996; 4,750,989; and 4,753,721.
It is, therefore, desirable to provide an improved resid hydrotreating unit (RHU) and process which overcomes most, if not all, of the above problems.